Optoelectronic device and the manufacturing method thereof

ABSTRACT

The present disclosure is related to an optoelectronic device comprising a semiconductor stack comprising a first surface and a second surface opposite to the first surface; a first contact layer on the first surface; and a second contact layer on the second surface, wherein the second contact layer is not overlapped with the first contact layer in a vertical direction; wherein the second contact layer comprises a plurality of dots separating from each other and formed of semiconductor material.

RELATED APPLICATION DATA

This application a continuation in-part application of U.S. patent application Ser. No. 15/467,679, filed Mar. 23, 2017, which is a continuation application of U.S. patent application Ser. No. 15/176,890, filed on Jun. 8, 2016, now U.S. Pat. No. 9,640,728, which is a continuation in-part application of U.S. patent application Ser. No. 14/852,212, filed on Sep. 11, 2015, now U.S. Pat. No. 9,385,272, which is a continuation application of U.S. patent application Ser. No. 14/489,169, filed Sep. 17, 2014, now U.S. Pat. No. 9,136,436, which is a continuation in-part application of U.S. patent application Ser. No. 13/932,661, filed Jul. 1, 2013, now U.S. Pat. No. 9,006,774, which is a continuation in-part application of U.S. patent application Ser. No. 13/528,059, filed Jun. 20, 2012, now U.S. Pat. No. 8,474,233, which is a continuation application of U.S. patent application Ser. No. 13/021,307, filed Feb. 4, 2011, now U.S. Pat. No. 8,207,550, which claims priority to U.S. Provisional Patent Application No. 61/302,662, filed on Feb. 9, 2010 under 35 U.S.C. § 119(e), the contents of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The application relates to an optoelectronic device and the manufacturing method thereof.

DESCRIPTION OF RELATED ART

Recently, efforts have been put to promote the luminous efficiency of the light-emitting diode (LED) in order to implement the device in the lighting field, and further conserve the energy and reduce carbon emission. The LED luminous efficiency can be increased through several aspects. One is to increase the internal quantum efficiency (IQE) by improving the epitaxy quality to enhance the combination efficiency of electrons and holes. Another is to increase the light extraction efficiency (LEE) that emphasizes on the increase of light which is emitted by the light-emitting layer capable of escaping outside the device, and therefore reducing the light absorbed by the LED structure.

SUMMARY

The present disclosure is related to an optoelectronic device comprising a semiconductor stack comprising a first surface and a second surface opposite to the first surface; a first contact layer on the first surface; and a second contact layer on the second surface, wherein the second contact layer is not overlapped with the first contact layer in a vertical direction; wherein the second contact layer comprises a plurality of dots separating to each other and formed of semiconductor material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1H illustrate the corresponding structures fabricated by the manufacturing method step-by-step in accordance with the first embodiment of the present disclosure.

FIG. 2 illustrates an optoelectronic device in accordance with the first embodiment of the present disclosure.

FIG. 3 illustrates an SEM photograph of the optoelectronic device in FIG. 2 in accordance with the present disclosure.

FIG. 4 illustrates a top view of the first ohmic contact layer and the second ohmic contact layer 140 in FIG. 2.

FIGS. 5A to 5E show the corresponding structures fabricated by the manufacturing method step-by-step in accordance with the second embodiment of the present disclosure.

FIG. 6 shows a top-view of the optoelectronic device in FIG. 5E.

FIGS. 7A to 7E show the corresponding structures fabricated by the manufacturing method step-by-step in accordance with the third embodiment of the present disclosure.

FIG. 8 illustrates a top view of an optoelectronic device in accordance with the fourth embodiment of the present disclosure.

FIG. 9A shows an enlarged detail of region I in FIG. 8.

FIG. 9B is a cross-sectional diagram along an A-A′ line of the optoelectronic device shown in FIG. 9A.

FIG. 10 shows a near field image of a part of the optoelectronic device shown in FIG. 8.

FIG. 11 shows another enlarged detail of region I in accordance with the fifth embodiment of the present disclosure.

FIG. 12A illustrates a top view of an optoelectronic device in accordance with the sixth embodiment of the present disclosure.

FIG. 12B is a cross-sectional diagram along a B-B′ line of the optoelectronic device shown in FIG. 12A.

FIGS. 13A to 13E show the corresponding structures fabricated by the manufacturing method step-by-step in accordance with the seventh embodiment of the present disclosure

FIG. 14 illustrates an optoelectronic device in accordance with the eighth embodiment of the present disclosure.

FIG. 15 illustrates an optoelectronic device in accordance with the ninth embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A to 1H show the corresponding structures fabricated by the manufacturing method step-by-step according to one embodiment of the present disclosure. With reference to FIG. 1A, the method for manufacturing an optoelectronic device in accordance with the present disclosure comprises a step of providing a substrate 101, such as a growth substrate for growing or carrying an optoelectronic system 120, and the material for the substrate 101 includes but is not limited to germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), gallium phosphide (GaP), sapphire, silicon carbide (SiC), silicon (Si), lithium aluminum oxide (LiAlO₂), zinc oxide (ZnO), gallium nitride (GaN), aluminum nitride (AlN) glass, composite, diamond, CVD diamond, diamond-like carbon (DLC), and so on.

A first window layer 111 is formed on the substrate 101 made of a material containing at least one element selected from the group consisting of Al, Ga, In, As, P, and N, such as GaN, AlGaInP or any other suitable materials. The first window layer 111 is a layer with a conductivity-type, such as n-type or p-type (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P where 0.5≤x≤0.8. The first window layer 111 has two opposite surface wherein the first surface of the first window layer 111 is closer to the substrate 101.

A transition layer could be optionally formed between the substrate 101 and the first window layer 111. The transition layer between two material systems can be used as a buffer system. For the structure of the light-emitting diode, the transition layer is used to reduce the lattice mismatch between two material systems. On the other hand, the transition layer could also be a single layer, multiple layers, or a structure to combine two materials or two separated structures where the material of the transition layer can be organic, inorganic, metal, semiconductor, and so on, and the structure can be a reflection layer, a heat conduction layer, an electrical conduction layer, an ohmic contact layer, an anti-deformation layer, a stress release layer, a stress adjustment layer, a bonding layer, a wavelength converting layer, a mechanical fixing structure, and so on.

Next, the optoelectronic system 120 is formed on the second surface of the first window layer 111 including at least a first layer 121 having a first conductivity-type, a conversion unit 122, and a second layer 123 having a second conductivity-type in sequence. The first layer 121 and the second layer 123 are two single-layer structures or two multiple layers structure (“multiple layers” means two or more than two layers) having different conductivities, electrical properties, polarities, and/or dopants for providing electrons or holes respectively. If the first layer 121 and the second layer 123 are composed of semiconductor materials, such as (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P where 0.5≤x≤0.8, the first or second conductivity-type can be p-type or n-type. The first window layer 111 has the same conductivity-type as the first layer 121, such as n-type. Besides, the first window layer 111 has greater impurity concentration than the first layer 121 to have a better conductivity. The conversion unit 122 disposed between the first layer 121 and the second layer 123 is a region where the light energy and the electrical energy could transfer or could be induced to transfer. The optoelectronic system 120, such as applied to a semiconductor device, equipment, product, circuit, can proceed or induce the light energy and electrical energy transfer. Specifically speaking, the optoelectronic system includes at least one of a light-emitting diode (LED), a laser diode (LD), a solar cell, a liquid crystal display, or an organic light-emitting diode. The optoelectronic system having the conversion unit 122 transferring the electrical energy to the light energy is a light-emitting diode, a liquid crystal display, or an organic light-emitting diode. The optoelectronic system having the conversion unit 122 transferring the light energy to the electrical energy is a solar cell or an optoelectronic diode. The phrase “optoelectronic system” in the specification does not require that all the sub-systems or units in the system manufactured by semiconductor materials. Other non-semiconductor materials such as metal, oxide, insulator, and so on could also be selectively integrated in this optoelectronic system 120.

Taking the light-emitting diode as an example, the emission spectrum of the transferred light could be adjusted by changing the physical or chemical arrangement of one layer or more layers in the optoelectronic system 120. The commonly used materials are the series of aluminum gallium indium phosphide (AlGaInP), the series of aluminum gallium indium nitride (AlGaInN), the series of zinc oxide (ZnO), and so on. The conversion unit 122 can be a single heterostructure (SH) structure, a double heterostructure (DH) structure, a double-side double heterostructure (DDH) structure, or a multi-quantum well (MWQ) structure. Specifically, the conversion unit 122 comprises a MQW structure comprising a plurality of barrier layers and well layers alternately stacked, each of the barrier layers comprises (Al_(y)Ga_((1-y)))_(0.5)In_(0.5)P where 0.5≤y≤0.8; and each of the well layers comprises In_(0.5)Ga_(0.5)P. Besides, the wavelength of the emitted light could also be adjusted by changing the number of the pairs of the quantum well or the composition of the barrier layer, e.g. the emitted light is red light with dominant wavelength between 600 and 630 nm by having y around 0.7 or amber light with dominant wavelength between 580 and 600 nm by having y around 0.55.

Forming a second window layer 112 on a first surface of the optoelectronic system 120 whose material contains at least one element selected from the group consisting of Al, Ga, In, As, P, and N, such as GaN, AlGaInP or any other suitable materials, and the second window layer 112 comprises at least one material different from the optoelectronic system 120 or the second layer 123. The second window layer 112 is preferred a layer with a conductivity-type the same as the second layer 123, such as a p-type GaP layer. In another embodiment, the sidewall of the second window layer 112 and/or the semiconductor system 120 need not be orthogonal to the substrate, but rather may be oblique thereto as indicated in FIG. 3.

Then, forming a first ohmic contact layer 130 formed by conductive material such as BeAu or GeAu alloy on the second window layer 112, and therefore forming a first stack structure 10 as shown in FIG. 1A, wherein the first ohmic contact layer 130 comprises a first portion 131 and a plurality of fingers 132 connecting the first portion 131 and extending toward borders of the first stack structure 10 as shown in FIG. 4. A first alloying process is then performed at an alloying temperature of around 300˜500° C. or more for forming an ohmic contact between the first ohmic contact layer 130 and the second window layer 112. The detail of the alloying process is well-known for those skilled in this field, and not necessarily disclosed herein.

Next, bonding a temporary substrate 102 formed by supportive material such as glass to the first ohmic contact layer 130 and the second window layer 112 of the first stack structure 10 as shown in FIG. 1B, and removing the substrate 101, and therefore exposing the first surface of the first window layer 111 as shown in FIG. 1C.

Next, forming a second ohmic contact layer 140 formed by conductive material like GeAu or BeAu alloy on the first surface of the first window layer 111, and therefore forming a second stack structure as shown in FIG. 1D, wherein the second ohmic contact layer 140 comprises a plurality of dots that are arranged in a two-dimensional array and is preferred substantially do not overlap with the first ohmic contact layer 130 in vertical direction as shown in FIG. 1D and for better current spreading effect. A second alloying process is then performed at an alloying temperature of around 300˜500° C. or more for forming an ohmic contact between the second ohmic contact layer 140 and the first window layer 111. The detail of the alloying process is well-known for those skilled in this field, and not necessarily disclosed herein.

Next, a transparent conductive layer 141 is sequentially formed by e-beam or sputtering to cover the second ohmic contact layer 140, wherein the material of the transparent conductive layer 141 comprises metal oxide, such as at least one material selected from the group consisting of indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide; and the thickness is about 0.005 μm˜0.6 μm, 0.005 μm˜0.5 μm, 0.005 μm˜0.4 μm, 0.005 μm˜0.3 μm, 0.005 μm˜0.2 μm, 0.2 μm˜0.5 μm, 0.3 μm˜0.5 μm, 0.4 μm˜0.5 μm, 0.2 μm˜0.4 μm, or 0.2 μm˜0.3 μm.

Next, a reflecting layer 150 is formed with a conductive material comprising metal, such as Ag, on the transparent conductive layer 141 as shown in FIG. 1E, and then the reflecting layer 150 is bonded to a supporting substrate 103 by a metal layer 160 as shown in FIG. 1F. In this embodiment, the supporting substrate 103 comprises Si, and the metal layer 160 served as a bonding layer comprises at least one material selected from the group consisting of In, Au, Sn, Pb, InAu, SnAu, and the alloy thereof.

Next, the temporary substrate 102 is removed to expose the first ohmic contact layer 130 and the second window layer 112, and therefore forming a third stack structure. Then the third stack structure is patterned by the lithographic-etching process to form a plurality of chip areas (not shown) on the supporting substrate 103, wherein the etchants of the etching process, e.g. dry-etching chemicals comprising fluoride or chloride etch the second window layer 112 relatively faster than the optoelectronic system 120 such that a first mesa region S1 is formed on the surface of the optoelectronic system 120 or the second layer 123, and the width of the optoelectronic system 120 or the second layer 123 is larger than the width of the second window layer 112 at the interface of the optoelectronic system 120 or the second layer 123 and the second window layer 112 as indicated in FIG. 1G. It can also be noted that a second mesa region S2 is formed on the surface of the first window layer 111, and the bottom width of the first window layer 111 is larger than the optoelectronic system 120 or the first layer 121.

Next, at least the exposed top and sidewall surfaces of the second window layer 112 is wet etched such that the exposed top and sidewall surfaces of the second window layer 112 are roughened, wherein the etching solution, such as a mixture of hydrofluoric acid (HF), nitric acid (HNO₃), and acetic acid (CH₃COOH), etches the second window layer 112 relatively faster than the optoelectronic system 120 such that the width difference L1 is further expanded and become larger, and the second window layer 112 has an enhanced surface roughness higher than that of the optoelectronic system 120, and wherein the width difference L1 is greater than 1 micron and/or less than 10 microns as indicated in FIG. 1H or FIG. 3.

Finally, a first pad 171 is formed on the first portion 131 of the first ohmic contact layer 130, a second pad 172 is formed on the supporting substrate 103, and a passivation layer 180 covers the second window layer 112 and the first ohmic contact layer 130 to form the optoelectronic device 1 a in accordance with the present disclosure as shown in FIG. 2. The passivation layer 180 serves as a protection layer to protect the optoelectronic device 1 a from environment damage, such as moisture, or mechanical damage. The SEM photograph of the optoelectronic device 1 a according to one embodiment of the present disclosure is demonstrated as in FIG. 3.

According to one embodiment of the present disclosure, the first window layer 111 comprises semiconductor material, such as (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P where 0.5≤x≤0.8, and the reflecting layer 150 comprising a metal element, e.g. Ag, is formed after the first and second alloying process such that the metal element in the reflecting layer 150 is less diffused into the first window layer 111, where the first window layer 111 comprises a semiconductor material, preferred a material with substantially the same composition as the first layer 121. According to another embodiment of the present disclosure, the atomic concentration of the metal element in the first window layer is less than 1*10¹⁷ cm⁻³ and the atomic concentration of the metal element is greater than 1*10¹⁶ cm⁻³, therefore causing less degradation to the reflecting layer 150. The reflecting layer 150 has a reflectivity greater than 90%.

Table 1 shows the optical efficiencies tested under given conditions by the optoelectronic device of the present disclosure. For an optoelectronic device with a small chip size, such as 10 mil², the optical efficiency is as high as about 70 lumen/watt under 20 mA or 0.2 mA/mil² of driving current. For an optoelectronic device with a relative smaller chip size, such as 14 mil², the optical efficiency is as high as about 100 lumen/watt under 20 mA or 0.1 mA/mil² of driving current. For an optoelectronic device with a relative larger chip size, such as 28 mil², the optical efficiency is as high as about 106 lumen/watt under 250 mA or 0.32 mA/mil² of driving current. For an optoelectronic device with a large chip size, such as 42 mil², the optical efficiency is as high as about 121 lumen/watt under 350 mA or 0.2 mA/mil² of driving current. It can be observed from table 1 that the optoelectronic device according to the embodiment of the present disclosure achieves an optical efficiency at least 70 lumen/watt, or preferred at least 100 lumen/watt at a driving current density ranging from 0.1˜0.32 mA/mil².

TABLE 1 the optical efficiencies tested under given conditions according to the optoelectronic device of the present disclosure. Chip Operating Current Optical Dominant size current density efficiency wavelength [mil²] [mA] [mA/mil²] [lumen/watt] [nm] 10 20 0.2 ~70 ~620 14 20 ~0.1 ~90 ~620 28 250 ~0.32 ~106 ~613 42 350 ~0.2 ~121 ~613

According to the present disclosure, the sheet resistance of the first window layer 111 is higher than that of the second window layer 112. Also, the second ohmic contact layer 140 substantially does not overlap with the first ohmic contact layer 130 in vertical direction. Therefore, the driving current is crowding nearby the second ohmic contact layer 140. The light emitted by the optoelectronic device is corresponding to the region of the second ohmic contact layer 140 and is not blocked by the first ohmic contact layer 130, and therefore having the effect of current blocking and benefit to lateral current spreading.

According to another embodiment of the present disclosure, the first window layer 111 comprises a lower impurity concentration than that of the second window layer 112 to have a lower sheet resistance than that of the second window layer 112. According to another embodiment of the present disclosure, the first window layer 111 comprises an n-type impurity with an impurity concentration of around 1×10¹⁷˜5×10¹⁷ cm⁻³, and the second window layer 112 comprises a p-type impurity with an impurity concentration of 1×10¹⁸˜5×10¹⁸ cm⁻³ higher than that of the first window layer 111. According to another embodiment of the present disclosure, the thickness of the first window layer 111 between 1˜5 microns is smaller than the thickness of the second window layer 112 between 5˜20 microns.

According to one embodiment of the present disclosure, because the sidewall surfaces of the second window layer 112 are roughened, the light can be laterally extracted easily. The chip areas can be rectangle in shape for better luminous efficiency. The ratio of the length to the width of the rectangle is preferred from 1.5:1 to 10:1.

As shown in FIGS. 5A to 5E, a method of manufacturing an optoelectronic device with different structure is disclosed in accordance with one embodiment. The method incorporates the steps as disclosed in FIGS. 1A˜1C and the descriptions thereof. The difference between the optoelectronic devices disclosed in FIG. 5E and in FIG. 2 is the structure between the first window layer 111 and metal layer 160.

Subsequent to the step of removing the substrate 101 and therefore exposing the first surface of the first window layer 111 as shown in FIG. 1C, a second ohmic contact layer 140 formed of conductive material like GeAu or BeAu alloy is formed on the first surface of the first window layer 111, as shown in FIG. 5A, wherein the second ohmic contact layer 140 comprises a plurality of dots that are arranged between any two fingers 132 which are parallel to each other and is preferred not substantially overlapped with the first ohmic contact layer 130 in vertical direction as shown in FIG. 6 so the current spreading is enhanced. As FIG. 6 shows, the pattern of the second ohmic contact layer 140 is aligned with the pattern of the first ohmic contact layer 130. Each of the plurality of dots has at least one bevel. The thickness of each of the dots is about 1000 Å˜10000 Å, and preferably is about 2000 Å˜6000 Å. A second alloying process is then performed at an alloying temperature of around 300˜500° C. or more for forming an ohmic contact between the second ohmic contact layer 140 and the first window layer 111. The detail of the alloying process is well-known to those skilled in this field, and not necessarily disclosed herein.

As shown in FIG. 5B, an insulating layer 142 is formed by e-gun or PECVD to conformably cover the second ohmic contact layer 140 and the first surface of the first window layer 111, wherein the insulating layer 142 is formed of insulating material with refractive index about 1.3˜1.6, such as SiO_(x) or MgF₂. The refractive index of the insulating layer 142 is at least 1.5 lower than that of the first window layer 111. The thickness of the insulating layer 142 is about 500 Å˜5000 Å, and preferably is about 500 Å˜1000 Å. The thickness of the insulating layer 142 is smaller than that of the second ohmic contact layer 140.

Next, as shown in FIG. 5C, the insulating layer 142 is regionally etched by dry etching, such as RIE, or wet etching, such as BOE (buffer oxide etch), to expose the second ohmic contact layer 140. After the etching, a portion of the first surface of the first window layer 111 can be exposed, too. The pattern of the contact layer is complementary to the pattern of the insulating layer.

Next, as shown in FIG. 5D, a transparent conductive layer 141 is formed to cover the insulating layer 142 and the second ohmic contact layer 140, wherein the material of the transparent conductive layer 141 comprises metal oxide, such as at least one material selected from the group consisting of indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide; and the thickness is about 50 Å˜150 Å. Then, a reflecting layer 150 is formed on the transparent conductive layer 141, wherein the material of the reflecting layer 150 comprises metal, such as Ag and the thickness is about 2500 Å˜7500 Å. The reflecting layer 150 dose not reach the border of the transparent conductive layer 141 and reveals the border region 1431 of the transparent conductive layer 141. In the embodiment, the transparent conductive layer 141 is served as an adhesion layer for improving the adhesion between the reflecting layer 150 and the insulating layer 142.

Then, the reflecting layer 150 is bonded to a supporting substrate 103 by a metal layer 160 and the following process is the same as aforementioned embodiment. The final structure of the optoelectronic device 1 b is shown in FIG. 5E. The reflecting layer 150 reveals the border region 1431, so a portion of the transparent conductive layer 141 is able to connect to the metal layer 160. In this embodiment, the supporting substrate 103 comprises Si, and the metal layer 160 served as a bonding layer comprises one material selected from the group consisting of In, Au, Sn, Pb, InAu, SnAu, and the alloy thereof. In the embodiment, the insulating layer 142 is capable of preventing the reflecting layer 150 from migrating to the first window layer 111 or the optoelectronic system 120 when an electrical current flows through the reflecting layer 150. The insulating layer 142 is also served as a current blocking. When the electrical current flows through the surface 1111, the electrical current can be blocked by the insulating layer 142 and passes through mainly the second ohmic contact layer 140. In the embodiment, the insulating layer 142 is disposed between the first window layer 111 and the reflecting layer 150, and since the difference of the refractive index between the first window layer 111 and the insulating layer 142 is larger than 1.5, the first window layer 111, the insulating layer 142 and the reflecting layer 150 are able to form an omnidirectional reflector (ODR) for reflecting the light emitted from the conversion unit 122. The reflectivity of the omnidirectional reflector (ODR) is larger than 95%, and preferably is larger than 97%.

FIGS. 7A to 7D show a method of manufacturing an optoelectronic device in accordance with third embodiment of the present disclosure.

The method incorporates the steps as disclosed in FIG. 1A˜1C and the descriptions thereof. Subsequent to the step of removing the substrate 101 and therefore exposing the first surface of the first window layer 111 as shown in FIG. 1C, a second ohmic contact region 140 a is formed on the first surface 110 of the first window layer 111 as shown in FIG. 7A. The second ohmic contact region 140 a comprises a plurality of dots formed of electrically conductive material like GeAu alloy or BeAu alloy and arranged between two of fingers 132 parallel to each other as shown in FIG. 6. The second ohmic contact region 140 a is not overlapped with the first ohmic contact layer 130 in vertical direction for enhancing the current spreading performance. Each of the plurality of dots has one bevel. The thickness of each of the dots is about 10 Å˜10000 Å, and preferably is about 50 Å˜6000 Å. Then, a second alloying process is performed at an alloying temperature of around 300˜500° C. or more for forming an ohmic contact between the second ohmic contact region 140 a and the first window layer 111. The detail of the alloying process is well-known to those skilled in this field, and not necessarily disclosed herein.

The first surface 110 of the first window layer 111 has a first portion 111 a exposed by the second ohmic contact region 140 a and a second portion 111 b contacting the second ohmic contact region 140 a. Then, the first portion 111 a of the first surface 110 is roughened by wet etching process using the second ohmic contact region 140 a as a mask such that the first portion 111 a has a first roughness (Ra) during 0.1 μm and 0.5 μm for scattering the light emitted from the conversion unit 122. The wet etching solution used for the wet etching process comprises an acid solution, such as HCl, H₃PO₄ or the combination thereof. In another embodiment, as shown in FIG. 7B, after roughening the first portion 111 a of the first surface 110, a platform 111 d is formed directly under each of the plurality of dots of the second ohmic contact region 140 a, and the area of the dot is smaller than that of the platform 111 d. The platform 111 d has substantially the same shape as the dot 111 d. The platform and the dot thereon are concentric. The platform 111 d comprises a peripheral region not covered by the dot wherein the peripheral region has a smaller roughness (Ra) than that of the first portion 111 a as shown in FIG. 7E, which is an SEM top-view image showing the topography of the roughened first portion 111 a, the platforms 111 d and the plurality of the dots of the second ohmic contact region 140 a. During the wet etching process, the etching solution penetrates into the first window layer 111 approximately at the border 140 a of the second ohmic contact region 140 a to thereby form a void 111 c in the first window layer 111 and surrounds the second ohmic contact region 140 a as shown in FIG. 7C. The void 111 c has a shrinking opening connecting to the border of the second ohmic contact region 140 a. The cross-section of the void 111 c is substantially a triangle or a triangle-like shape and one vertex of the triangle connects to the border of the second ohmic contact region 140 a. Each of the edges of the triangle is smaller than 2 μm and two angles θ₁ and θ₂ between the two edges and the first surface 110 respectively are different. The void 111 c contains air therein. In another embodiment, the cross-sectional shape of the void 111 c comprises an oval.

As shown in FIG. 7C, the method further comprises forming a transparent layer 145 on the first portion 111 a and not covering the second ohmic contact region 140 a. During forming the transparent layer 145, the material of the transparent layer 145 may partially deposit into the void 111 c through the shrinking opening of the void 111 c. The pattern of the transparent layer 145 is complementary to the pattern of the second ohmic contact region 140 a from the top view of the optoelectronic device 1 c as shown in FIG. 7D. The thickness of the transparent layer 145 is between 0.05 μm and 2.5 μm, and preferably has the same thickness as the second ohmic contact region 140 a. The difference between a thickness of the transparent layer 145 and that of the second ohmic contact region 140 a is preferably smaller than 1 μm for reducing the height between the surface of the transparent layer 145 and the second ohmic contact region 140 a. The transparent layer 145 comprises insulating transparent material with a refractive index small than 2, such as SiN_(x), AlO_(x), SiO_(x) or MgF_(x), or conductive transparent oxide material with a refractive index small than 2.2, such as indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide (IZO), zinc aluminum oxide (AZO), and zinc tin oxide. The refractive index of the transparent layer 145 is different from that of the void 111 c, and the refractive indices of the void 111 c and the transparent layer 145 are both at least 1.0 lower than that of the first window layer 111 for improving the light-extraction efficiency of the conversion unit 122.

As shown in FIG. 7D, the method further comprises forming a reflecting layer 150 conformably covering the second ohmic contact region 140 a and the transparent layer 145 for forming an omnidirectional reflecting structure 144. Since the void 111 c embeds air having a refractive index about 1 and the refractive index difference between the void 111 c and the first window layer 111 is larger than 2, the omnidirectional reflecting structure 144 provides a reflectivity larger than 90% for the light emitted from the conversion unit 122, and preferably larger than 95%. Before forming the reflecting layer 150, the method optionally comprises flattening the transparent layer 145 for further enhancing the reflectivity of the omnidirectional reflecting structure 144. The thickness of the reflecting layer 150 is between 0.1 μm and 1 μm, and preferably is between 0.3 μm and 0.5 μm. The material of the reflecting layer 150 comprises Ag, Au or Al. Then, a barrier layer 151 is formed to conformably cover the reflecting layer 150 for preventing the material of the reflecting layer 150 from migrating when an operating current flows through the reflecting layer 150 and therefore deteriorate the reflectivity of the reflecting layer 150 and the reliability of the optoelectronic device. The thickness of the barrier 151 is between 0.5 μm and 5 μm, and preferably is between 0.5 μm and 1.5 μm. The material of the barrier layer 151 comprises Ni, Ti, Pt, Au or the combination thereof.

Then the barrier 151 is bonded to a supporting substrate 103 by a metal layer 160. In one embodiment, the supporting substrate 103 comprises Si, and the metal layer 160 served as a bonding layer comprises at least one material selected from the group consisting of In, Au, Sn, Pb, InAu, SnAu, and the alloy thereof. The subsequent steps of the method are very similar to or the same as the steps as described in FIGS. 1F˜1H the descriptions thereof, the entirety of which are incorporated into the present embodiment. For example, the temporary substrate 102 is removed to expose the first ohmic contact layer 130 and the second window layer 112, and therefore forming a stack structure. Then the stack structure is patterned by the lithographic-etching process to form a plurality of chip areas (not shown) on the supporting substrate 103, wherein the etchants of the etching process, e.g. dry-etching chemicals comprising fluoride or chloride etch the second window layer 112 relatively faster than the optoelectronic system 120 such that a first mesa region S1 is formed on the surface of the optoelectronic system 120 or the second layer 123, and the width of the optoelectronic system 120 or the second layer 123 is larger than the width of the second window layer 112 at the interface of the optoelectronic system 120 or the second layer 123 and the second window layer 112. It can also be noted that a second mesa region S2 is formed on the surface of the first window layer 111, and the bottom width of the first window layer 111 is larger than the optoelectronic system 120 or the first layer 121. Next, at least the exposed top and sidewall surfaces of the second window layer 112 is wet etched such that the exposed top and sidewall surfaces of the second window layer 112 are roughened, wherein the etching solution, such as a mixture of hydrofluoric acid (HF), nitric acid (HNO₃), and acetic acid (CH₃COOH), etches the second window layer 112 relatively faster than the optoelectronic system 120 such that the width difference L1 is further expanded and become larger, and the second window layer 112 has an enhanced surface roughness higher than that of the optoelectronic system 120, and wherein the width difference L1 is greater than 1 micron and/or less than 10 microns as indicated in FIG. 7D or FIG. 3. Finally, a first pad 171 is formed on the first ohmic contact layer 130, a second pad 172 is formed on the supporting substrate 103, and a passivation layer 180 covers the second window layer 112 and the first ohmic contact layer 130 to form the optoelectronic device 1 c in accordance with the present disclosure as shown in FIG. 2. The passivation layer 180 serves as a protection layer to protect the optoelectronic device from environment damage, such as moisture, or mechanical damage.

FIG. 7D shows an optoelectronic device 1 c with the omnidirectional reflecting structure 144 in accordance with the present disclosure. The optoelectronic device 1 c comprises the first window layer 111, the optoelectronic system 120 on a second surface of the first window layer 111, the second window layer 112 on a first surface of the optoelectronic system 120, the second ohmic contact region 140 a on the first surface of the first window layer 111, the omnidirectional reflecting structure 144 on the second ohmic contact region 140 a and the first surface of the first window layer 111, the barrier 151 completely covering the omnidirectional reflecting structure 144, the metal layer 160 bonding the supporting substrate 103 and the barrier 151, the first ohmic contact layer 130 on the second window layer 112, the first pad 171 on the first ohmic contact layer 130, the second pad 172 on the supporting substrate 103, and the passivation layer 180 covering the second window layer 112 and the first ohmic contact layer 130. The optoelectronic system 120 includes at least the first layer 121 having a first conductivity-type, the conversion unit 122, and the second layer 123 having a second conductivity-type. the omnidirectional reflecting structure 144 includes the void 111 c in the first window layer 111 and surrounding the second ohmic contact region 140 a, the transparent layer 145 on the first surface of the first window layer 112 not covered by the second ohmic contact region 140 a, the reflecting layer 150 conformably covering the second ohmic contact region 140 a and the transparent layer 145.

The first window layer 111 is made of a material containing at least one element selected from the group consisting of Al, Ga, In, As, P, and N, such as GaN, AlGaInP or any other suitable materials. The second window layer 112 comprises at least one material different from the second layer 123, and is preferred a layer with a conductivity-type the same as the second layer 123, such as a p-type GaP layer. The first mesa region S1 is on the surface of the optoelectronic system 120 or the second layer 123, and the width of the optoelectronic system 120 or the second layer 123 is larger than the width of the second window layer 112 at the interface of the optoelectronic system 120 or the second layer 123 and the second window layer 112. The second mesa region S2 is on the surface of the first window layer 111, and the bottom width of the first window layer 111 is larger than the optoelectronic system 120 or the first layer 121. The top and sidewall surfaces of the second window layer 112 are roughened such that the second window layer 112 has an enhanced surface roughness higher than that of the optoelectronic system 120. The width difference L1 between the optoelectronic system 120 and the first window layer 111 is greater than 1 micron and/or less than 10 microns. The second ohmic contact region 140 a having a plurality of dots ohmically contacts with the first window layer 111 and reveals the first portion 111 a. The first portion 111 a is roughened to have a first roughness (Ra) during 0.1 μm˜0.5 μm for scattering the light emitted from the conversion unit 122. The shrinking opening of the void 111 c connects to the border 140 a of the second ohmic contact region 140 a. The cross-section of the void 111 c is substantially a triangle or a triangle-like shape and one vertex of the triangle connects to the border 140 a. The pattern of the transparent layer 145 on the first portion 111 a is complementary to the pattern of the second ohmic contact region 140 a from the top view of the optoelectronic device 1 c. The refractive index of the transparent layer 145 is different from that of the void 111 c, and the refractive indices of the void 111 c and the transparent layer 145 are both at least 1.0 lower than that of the first window layer 111 for improving the light-extraction efficiency of the conversion unit 122. The reflecting layer 150 conformably covers the second ohmic contact region 140 a and the transparent layer 145 for forming an omnidirectional reflecting structure 144. Since the void 111 c embeds air having a refractive index about 1 and the refractive index difference between the void 111 c and the first window layer 111 is larger than 2, the omnidirectional reflecting structure 144 provides a reflectivity larger than 95% for the light emitted from the conversion unit 122, and preferably larger than 97%. Before forming the reflecting layer 150, the transparent layer 145 is flatted for further enhancing the reflectivity of the omnidirectional reflecting structure 144. The thickness of the reflecting layer 150 is between 0.1 μm˜1 μm, and preferably is between 0.3 μm˜0.5 μm. The thickness of the barrier 151 completely covering the reflecting layer 150 is between 0.5 μm˜5 μm, and preferably is between 0.5 μm˜1.5 μm such that the barrier 151 is able to prevent the reflecting layer 150 from migrating.

FIG. 8 illustrates a top view of an optoelectronic device in accordance with the fourth embodiment of the present disclosure. FIG. 9A shows an enlarged detail of region I in FIG. 8. FIG. 9B is a cross-sectional diagram along an A-A′ line of the optoelectronic device shown in FIG. 9A. The optoelectronic device in accordance with the fourth embodiment of the present disclosure comprises substantially the same structure as the third embodiment, and the difference is as follows. The supporting substrate 103 comprises a first side 1031 having a first length L₁, a second side opposite to the first side and having a second length L₂, a third side and a fourth side between the first side and the second side, wherein the third side has a third length L₃, and the fourth side has a fourth length L₄. The optoelectronic device comprises two first pads 171 and multiple fingers 132 extending from the first pads 171 toward at least one of the sides of the supporting substrate 103. In the present embodiment, the first pads 171 are nearer the first side 1031 than the second side 1032. At least one of the multiple fingers 132 extends from the first pads 171 toward the second side 1032, wherein the finger 132 is substantially parallel to the third side 1033 and the fourth side 1034. Referring to FIG. 9B, multiple recesses are formed in the transparent layer 145 and are separated to one another. Therefore, the pattern of the recesses is complementary to the pattern of the transparent layer 145. The second ohmic contact layer 140 is formed conformably on the transparent layer 145 and filled in the multiple recesses. The part of the second ohmic contact layer 140 directly in contact with a first semiconductor layer 111, which is the window layer 111 in the present embodiment, forms an ohmic contact with the first window layer 111, and thus forms multiple contact regions 140 b. The thickness of the transparent layer 145 is about 500 Å˜5000 Å, and preferably is about 1000 Å˜2000 Å. The multiple contact regions 140 b are separated from one another. The contact regions 140 b do not overlap any of the fingers in vertical direction. As shown in FIG. 9A, a first contact region 140 b ₁ in the multiple contact regions 140 b is between two adjacent fingers 132 a,132 b in the multiple fingers 132, and a first distance D₁ between the first contact region 140 b ₁ and one of the adjacent fingers 132 a is between 0.8% and 5%, and preferably, between 1% and 3% of one of the lengths of the substrate. Preferably, the other adjacent fingers 132 b and the contact region 140 b ₁ are separated by the first distance D₁ as well. In the present embodiment, the first length L₁, the second length L₂, the third length L₃ and the fourth length L₄ are substantially the same, for example, between about 1055 and 1090 μm. In one embodiment, the shape of the supporting substrate 103 is rectangle. Therefore, the first length L₁ is substantially the same as the second length L₂, and the third length L₃ is substantially the same as the fourth length L₄. An angle between one of the fingers 132 and the first side 1031 or the second side 1032 is between 85 degrees and 95 degrees. In the present embodiment, the first distance D₁ is between 10 μm and 30 μm, and preferably, between 13 μm and 26 μm. The shape of the supporting substrate 103 is not limited to the present embodiment. In the present disclosure, each finger 132 has a longer side and a shorter side compared to the longer side, and a width w1 of the shorter side is between 3 μm and 12 μm, and preferably, between 4 μm and 6 μm. The pattern or the shape of the fingers is not limited to the present embodiment, for example, one of the fingers may be a curve or an annular, and the finger and the closest contact region is spaced apart by the first distance D₁.

In the present embodiment, each contact region 140 b comprises multiple contact areas 140 c separated from one another and arranged in multiple columns along a direction parallel to one of the two adjacent fingers 132. In the present embodiment, the multiple contact areas 140 c ₁ in the first contact region 140 b ₁ are arranged in three columns along the direction parallel to the two adjacent fingers 132 a, 132 b. Specifically, the contact areas 140 c ₁ are arranged in a staggered pattern. A second distance D₂ between two adjacent columns in the multiple columns of the first contact region 140 b ₁ is shorter than the first distance D₁. The second distance D₂ is between 3 μm and 10 μm, and preferably, between 4 μm and 7 μm. Preferably, a ratio of the second distance D₂ to the first distance D₁ is between 0.1 and 0.7, and preferably between 0.15 and 0.55. More preferably, a difference between the second distance D₂ and the first distance D₁ is between 3 μm and 25 μm, and preferably between 6 μm and 22 μm.

In the present embodiment, as shown in FIG. 8, the shape of each contact area 140 c is circle and is substantially the same as one another. However, the shape of the contact area 140 c is not limited to the present embodiment. The contact area 140 c has a width between 5 μm and 15 μm, and preferably, between 7 μm and 10 μm. In the present embodiment, the width is the diameter of the circle. In the present embodiment, each interval between two adjacent contact areas 104 c in the same column is substantially the same as one another, for example, between 5 μm and 15 μm, and preferably, between 5 μm and 10 μm. In one embodiment, each interval between two adjacent contact areas 140 c in the adjacent columns respectively is substantially the same as one another. The arrangement of the contact areas 104 c is not limited to the present embodiment, for example, one of the intervals between two adjacent contact areas 140 c in the same column or in the adjacent columns respectively can be different from those of the others, the width of one of the contact areas 140 c can be different from those of the others and/or the number of the columns can be changed.

In one embodiment, the second ohmic contact layer 140 comprises transparent conducive oxide material comprising indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide (CTO), antimony tin oxide (ATO), aluminium zinc oxide (AZO), zinc tin oxide (ZTO), gallium doped zinc oxide (GZO), tungsten doped indium oxide (IWO), zinc oxide (ZnO), or indium zinc oxide (IZO). In the present embodiment, the second ohmic contact layer 140 comprises indium tin oxide (ITO). The second ohmic contact layer 140 has a thickness not less than 20 Å, and preferably, not greater than 2000 Å, and more preferably, not greater than 200 Å.

In one embodiment, the optoelectronic device further comprises a current spreading layer 170 between the reflecting layer 150 and the second ohmic contact layer 140. The material of the current spreading layer 170 comprise transparent conductive oxide material comprising indium tin oxide (ITO), aluminum zinc oxide (AZO), SnCdO, antimony tin oxide (ATO), ZnO, Zn₂SnO₄ (ZTO) or indium zinc oxide (IZO). The current spreading layer 170 has a thickness between 1000 Å and 5000 Å, and preferably between 1500 Å and 3500 Å. The material of the current spreading layer 170 can be the same or different from the material of the second ohmic contact layer 140. Preferably, the material of the current spreading layer 170 is different from the material of the second ohmic contact layer 140. In the present embodiment, the current spreading layer 170 comprises IZO.

FIG. 10 shows a near field image of a part of the optoelectronic device shown in FIG. 8. As shown in FIG. 10, the light is concentrated more substantially around the area where the contact regions 140 b are located. Therefore, the light is less likely to be hindered by the fingers 132.

In one embodiment, the first distance D₁ between the first contact region 140 b ₁ and one of the adjacent fingers 132 a is between 5% and 50%, and preferably, between 10% and 40%, and more preferably, between 10% and 25% of a third distance D3 between the two adjacent fingers. In the present embodiment, the third distance D₃ is between 60 μm and 150 μm, and preferably, between 70 μm and 130 μm. Specifically, the third distance D₃ is between 5% and 15%, and more preferably, between 6% and 13% the first length L₁ of the substrate.

In one embodiment, a first finger 132 b in the multiple fingers 132 is between two of the adjacent contact regions 140 b, and a fourth distance D₄ between the two adjacent contact regions 140 b is between 0.8% and 8%, and preferably, between 1.5% and 6% of one of the length of the substrate. Preferably, the fourth distance D₄ between the two adjacent contact regions 140 b is between 0.8% and 8%, and preferably, between 1.5% and 6% of the first length L1 of the first side 1031 or the second length L₂ of the second side 1032. In the present embodiment, the fourth distance D₄ is between 10 μm and 70 μm, and preferably, between 20 μm and 60 μm.

FIG. 11 shows another enlarged detail of region I in accordance with the fifth embodiment of the present disclosure. An optoelectronic device in accordance with the fifth embodiment of the present disclosure comprises substantially the same structure as the fourth embodiment, and the difference is that the multiple contact areas 140 c in at least one of the contact regions 140 b are arranged in four columns along the direction parallel to the two adjacent fingers 132 a, 132 b.

FIG. 12A illustrates a top view of an optoelectronic device in accordance with the sixth embodiment of the present disclosure. FIG. 12B is a cross-sectional diagram along a B-B′ line of the optoelectronic device shown in FIG. 12A. The optoelectronic device in accordance with the sixth embodiment of the present disclosure comprises substantially the same structure as the fourth embodiment, and the difference is that the each contact region 140 b is a continuous structure without comprising multiple contact areas 140 c as mentioned in the fourth embodiment, wherein the contact regions 140 b are separated from one another. In the present embodiment, the shape of each contact region 140 b is quadrangle and extending along a direction parallel to the two adjacent fingers 132. The shape of the contact region 140 b is not limited to the present embodiment, for example, the shape of the contact region can be circle.

In one embodiment, the first window layer 111 has the same conductivity-type as the first layer 121, such as p-type. The second window layer 112 is a layer comprising n-type (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P where x is near or substantially equal to 1.

Compared to a conventional optoelectronic device, the optoelectronic device of the present disclosure has a higher radiant power. Specifically, the radiant power of the optoelectronic device of the present disclosure has increased by near 10% compared to a conventional optoelectronic device.

In one embodiment, the optoelectronic device is devoid of the first window layer 111 between the first layer 121 and the transparent layer 145. The optoelectronic device further comprises a first semiconductor contact layer (not shown) between the first layer 121 and the transparent layer 145. The conductivity type of the first semiconductor contact layer is the same as that of the first layer 121. In one embodiment, the first semiconductor contact layer is p-type and has a high p-type impurity concentration, such as greater than 10×¹⁷/cm³, and preferably, greater than 10×¹⁸/cm³, and more preferably, between 1×10¹⁹/cm³ and 5×10²²/cm³ both inclusive. The material of the contact layer comprises a Group III-V semiconductor material, such as GaP. In the present embodiment, the first semiconductor contact layer is the first semiconductor layer to be in contact with the second ohmic contact layer 140. The first semiconductor contact layer has a thickness between 10 nm and 100 nm, and preferably between 10 nm and 60 nm. In one embodiment, the optoelectronic device further comprises a buffer layer (not shown) between the first layer 121 and the first semiconductor layer. The buffer layer has a bandgap smaller than that of the first layer 121. Preferably, the content of Al in the buffer layer is less than that of the first layer 121. More preferably, the buffer layer comprises (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≤x≤1, 0≤y≤1, and preferably, 0.49≤x≤0.51, 0≤y≤0.5. In the present embodiment, the first layer 121 comprises (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein x is near or substantially equal to 1. The buffer layer has a thickness between 30 nm and 200 nm, and preferably, between 30 nm and 100 nm. The buffer layer is for preventing the first layer 121 from being damaged during the manufacturing process. Specifically, a distance between the first layer 121 and the transparent layer 145 is between 40 nm and 400 nm, and preferably between 60 nm and 200 nm, and more preferably, between 60 nm and 100 nm. The radiant power of the optoelectronic device of the present embodiment has increased by near 5% compared to the optoelectronic device of the fourth embodiment.

In one embodiment, the optoelectronic device further comprises a second semiconductor contact layer 190 between the fingers 132 and the second window layer 112. The second semiconductor contact layer 190 has a pattern substantially the same as the pattern of the fingers 132. The fingers 132 forms a low specific contact resistance or an ohmic contact with the second semiconductor contact layer 190, wherein the specific contact resistance between the fingers 132 and the second semiconductor contact layer 190 is lower than 10⁻² ohm(Ω)cm², and preferably, lower than 10⁻⁴ Ωcm². Specifically, the second semiconductor contact layer 190, which is the first semiconductor layer directly contacting the fingers 132, is for reducing the resistance across the fingers 132 comprising metal and the second semiconductor contact layer 190 such that the forward voltage of the optoelectronic device is less than 1.3×1240/λ (volt), wherein λ is the peak wavelength. The conductivity type of the second semiconductor contact layer 190 is the same as that of the second window layer 112. In one embodiment, the second semiconductor contact layer 190 is n-type and has a high n-type impurity concentration, such as greater than 10×¹⁸/cm3, and preferably, greater than 10×¹⁹/cm³, and more preferably, between 1×10¹⁹/cm³ and 5×10²²/cm³ both inclusive. The material of the contact layer comprises a Group III-V semiconductor material, such as GaAs, AlGaAs.

The first pad 171 and the second pad 172 are for electrically connected to an external power source and for conducting a current therebetween. The first pad 171, the second pad 172 and/or the fingers 132 may further comprise a layer comprising transparent conductive material or metal material, wherein the transparent conductive material comprises transparent conductive oxide, and wherein the metal material comprises Au, Pt, GeAuNi, Ti, BeAu, GeAu, Al, or ZnAu, Ni.

In one embodiment, the second ohmic contact layer 140 in FIG. 2 and in FIG. 5E and the second ohmic contact region 140 a in FIG. 7D can have substantially the same arrangement as that of the contact regions 140 b as shown in FIG. 8 or FIG. 12A.

In the present disclosure, if not specifically mention, the general expression of AlGaAs means Al_(x)Ga_((1-x))As, wherein 0≤x≤1; the general expression of AlInP means Al_(x)In_((1-x))P, wherein 0≤x≤1; the general expression of AlGaInP means (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≤x≤1, 0≤y≤1; the general expression of AlGaN means Al_(x)Ga_((1-x))N, wherein 0≤x≤1; the general expression of AlAsSb means AlAs_((1-x))Sb_(x) wherein 0≤x≤1 and the general expression of InGaP means In_(x)Ga_(1-x)P, wherein 0≤x≤1. The content of the element can be adjusted for different purposes, such as, but not limited to, adjusting the energy gap or adjusting the peak wavelength or the dominant wavelength.

Subsequent to the step of removing the substrate 101 and therefore exposing the first surface of the first window layer 111 as shown in FIG. 1C, as shown in FIGS. 13A to 13E, a method of manufacturing an optoelectronic device 1 d with different structure is disclosed in accordance with the seventh embodiment. The method incorporates the steps as disclosed in FIGS. 1A to 1C and the descriptions thereof.

In the seventh embodiment, the first window layer 111 comprises semiconductor material, such as (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P, where 0.5≤x≤1, and the second window layer 112 comprises semiconductor material, such as (Al_(y)Ga_((1-y)))_(0.5)In_(0.5)P where 0.5≤y≤1, wherein the second window layer 112 and the first window layer 111 have different conductivity-types, for example, the first window layer 111 is n-type and the second window layer 112 is p-type, or the second window layer 112 is n-type and the first window layer 111 is p-type. The thickness of the first window layer 111 is equal to or smaller than the thickness of the second window layer 112, wherein the thickness of the first window layer 111 is between 1˜5 microns and the thickness of the second window layer 112 is between 1˜10 microns.

The first layer 121 and the second layer 123 are two single-layer structures or two multiple layers structure (“multiple layers” means two or more layers) having different conductivities, electrical properties, polarities, and/or dopants for providing electrons or holes respectively. The first layer 121 and the second layer 123 are composed of semiconductor materials, such as (Al_(x)Ga_((1-x)))_(0.5)In_(0.5)P where 0.5<x≤0.8, and the first or second conductivity-type can be p-type or n-type. The first window layer 111 and the first layer 121 have the same conductivity-type, and the second window layer 112 and the second layer 123 have the same conductivity-type. In the seventh embodiment, the conversion unit 122 comprises a MQW structure comprising a plurality of barrier layers and well layers alternately stacked for emitting a light, wherein each of the barrier layers comprises (Al_(y)Ga_((1-y)))_(0.5)In_(0.5)P where 0<y≤0.5, and each of the well layers comprises In_(0.5)Ga_(0.5)P.

In the seventh embodiment, as shown in FIG. 13A, a second ohmic contact layer 140′ formed of semiconductor material, such as GaP, is formed on a surface 111S of the first window layer 111. Because the semiconductor material, such as GaP, is substantially transparent for the light emitted from the conversion unit 122, at least a part of the light is able to penetrate the second ohmic contact layer 140′ for improve the light extraction efficiency of the optoelectronic device 1 d.

In the seventh embodiment, the method of forming the second ohmic contact layer 140′ comprises an etching process such as wet etching and dry etching. The first window layer 111 with the thickness between 1˜5 microns is able to prevent the optoelectronic system 120 from being etched during the process of forming the second ohmic contact layer 140′.

The second ohmic contact layer 140′ has greater impurity concentration than the first window layer 111 to have a better conductivity than the first window layer 111. In a top view as shown in FIG. 4, 6 or 8, the second ohmic contact layer 140′ may comprise a plurality of dots that are arranged around fingers 132 or between any two adjacent fingers 132 which are substantially parallel to each other, and is preferred not substantially overlapped with the first ohmic contact layer 130 in a vertical direction as shown in FIG. 13A. In the seventh embodiment, the second ohmic contact layer 140′ can have substantially the same arrangement and the same width as that of the contact regions 140 b as shown in FIG. 8 or 12A or that of the second ohmic contact layer 140 in FIG. 4 or 6, so the current spreading can be enhanced. As shown in FIG. 6, 8 or 12A, the pattern of the second ohmic contact layers 140′ may be arranged along or around the pattern of the fingers 132. As shown in FIG. 13A, each of the plurality of dots of the second ohmic contact layer 140′ has a side surface 140S′ and there may be an obtuse angle α between the side surface 140S′ and the surface 111S. In another embodiment, the side surface 140S′ of at least one of the dots of the second ohmic contact layer 140′ may be about perpendicular to the surface 111S. In the seventh embodiment, the thickness of the second ohmic contact layer 140′ is about 100 Å˜10000 Å, and preferably is about 100 Å˜5000 Å for better uniformity of the second ohmic contact layer 140′.

In the seventh embodiment, the method of forming the second ohmic contact layer 140′ comprises epitaxially growing a semiconductor layer (not shown) on the first window layer 111, and patterning the semiconductor layer to expose the surface 111S of the first window layer 111 and form the second ohmic contact layer 140′ as shown in FIG. 13A by a removing method such as wet etching and dry etching. Since the second ohmic contact layer 140′ is made of semiconductor material, the alloying process is not necessary for forming an ohmic contact between the second ohmic contact layer 140′ and the first window layer 111. Additionally, in one embodiment, the impurity concentration of the second ohmic contact layer 140′ increases in the direction from the first window layer 111 toward the second ohmic contact layer 140′ or in a direction from the optoelectronic system 120 toward the second contact layer 140′, wherein the highest impurity concentration of the second ohmic contact layer 140′ is equal to or larger than 1*10¹⁹ cm⁻³, and the lowest impurity concentration of the second ohmic contact layer 140′ is equal to or lower than 1*10¹⁸ cm⁻³.

Next, as shown in FIG. 13B, an insulating layer 142 may cover or substantially conformably cover the second ohmic contact layer 140′ and the surface 111S of the first window layer 111 by a coating method such as e-gun and PECVD, wherein the insulating layer 142 comprises insulating material with refractive index about 1.3˜1.6, such as SiO_(x) or MgF₂. In the seventh embodiment, the refractive index of the insulating layer 142 is at least 1.5 lower than that of the first window layer 111, which means the refractive index of the first window layer 111 is equal to or larger than 2.8. The thickness of the insulating layer 142 may be smaller or larger than that of the second ohmic contact layer 140′, wherein the thickness of the insulating layer 142 is about 500 Å˜5000 Å, and preferably is about 500 Å˜2000 Å.

Next, as shown in FIG. 13C, the insulating layer 142 is regionally removed by a removing method such as etching process and lift-off process to expose the second ohmic contact layer 140′, wherein the etching process comprises dry etching, such as RIE, or wet etching, such as BOE (buffer oxide etch). After regionally removing the insulating layer 142, the insulating layer 142 contacts the side surface 140S′ of at least one of the dots of the second ohmic contact layer 140′, and the surface 111S of the first window layer 111 is fully covered by the insulating layer 142 and the second ohmic contact layer 140′. The interface between the insulating layer 142 and the side surface 140S′ of each of the dots of the second ohmic contact layer 140′ is able to reflect the light emitted from the conversion unit 122 to improve the light-extraction efficiency. In one embodiment, the insulating layer 142 may cover the side surface 140S′ and a portion of a top surface 140T′ of one of the dots of the second ohmic contact layer 140′, wherein the top surface 140T′ may be substantially parallel to the surface 111S of the first window layer 111 of one of the dots of the second ohmic contact layer 140′. In one embodiment, from the top view of the second ohmic contact layer 140′ and the insulating layer 142, the pattern of the second ohmic contact layer 140′ may be complementary to the pattern of the insulating layer 142.

Next, as shown in FIG. 13D, a conductive layer 141 which may be transparent is formed to cover or substantially conformally cover the insulating layer 142 and the second ohmic contact layer 140′ to electrically connect the second ohmic contact layer 140′ by contacting the top surface 140T′ of the dot of the second ohmic contact layer 140′. The material of the transparent conductive layer 141 comprises metal oxide, such as indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide; and the thickness of the transparent conductive layer 141 is about 50 Å˜150 Å. Next, another conductive layer 141′ may be formed to cover or substantially conformally cover the transparent conductive layer 141. In the seventh embodiment, a surface 141S′ of the conductive layer 141′ opposite to the conductive layer 141 is polished into a flat surface, wherein the roughness average (Ra) of the surface 141S′ is equal to or lower than 2 nm. The conductive layer 141′ comprises metal oxide which may be the same as or different from that of the conductive layer 141, such as indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide; and the thickness of the conductive layer 141′ is about 10 nm˜1000 nm. In the seventh embodiment, the conductive layer 141 and the conductive layer 141′ are made of different material, for example, the conductive layer 141 may be made of indium tin oxide (ITO) and the conductive layer 141′ may be made of indium zinc oxide. Then, a reflecting layer 150 is formed on the surface 141S′ of the transparent conductive layer 141′, wherein the material of the reflecting layer 150 comprises metal, such as Ag and Au; and the thickness of the reflecting layer 150 is about 2500 Å˜7500 Å.

Then, the reflecting layer 150 is bonded to a supporting substrate 103 by a metal layer 160 and the following process is the same as aforementioned embodiments in the present disclosure. After the processes described in the present disclosure, a structure of the optoelectronic device 1 d is formed as shown in FIG. 13E. In the seventh embodiment, the supporting substrate 103 comprises Si, and the metal layer 160 served as a bonding layer comprises one material selected from the group consisting of In, Au, Sn, Pb, InAu, SnAu, and the alloy thereof. The thickness of the metal layer 160 is between 1˜10 μm both inclusive. In one embodiment, the metal layer 160 is formed by two layer bonded together, and the metal layer 160 comprises a bonding interface or a void between the two layers. In the seventh embodiment, the insulating layer 142 is served as a current blocking. When the electrical current flows through the optoelectronic device 1 d, the electrical current can be blocked by the insulating layer 142 and mainly pass through the second ohmic contact layer 140′. In the seventh embodiment, the insulating layer 142 is disposed between the first window layer 111 and the reflecting layer 150, and the first window layer 111, the insulating layer 142, the conductive layer 141, the conductive layer 141′ and the reflecting layer 150 together may function as an omnidirectional reflector (ODR) for increasing the reflection of light emitted from the conversion unit 122. The reflectivity of the omnidirectional reflector is larger than 95%, and preferably is larger than 97%.

As shown in FIG. 14, an optoelectronic device 1 e is disclosed in accordance with the eighth embodiment. The method for manufacturing the optoelectronic device 1 e incorporates the steps as disclosed in FIGS. 1A˜1C, 13A˜13E and the descriptions thereof. The major difference between the optoelectronic device 1 e and the optoelectronic device 1 d is the structure of the second ohmic contact layer 140′.

In the eighth embodiment, the second ohmic contact layer 140′ comprises a first doping layer 140 a contacting the surface 111S and a second doping layer 140 b on the first doping layer 140 a. The first doping layer 140 a and the second doping layer 140 b together may be a tunnel junction structure, wherein the first doping layer 140 a and the first window layer 111 have the same conductivity-type, and the second doping layer 140 b and the first window layer 111 have different conductivity-types. For example, the first doping layer 140 a and the first window layer 111 are p-type, and the second doping layer 140 b is n-type, or the first doping layer 140 a and the first window layer 111 are n-type, and the second doping layer 140 b is p-type. The lowest impurity concentrations of the first doping layer 140 a and the second doping layer 140 b are equal to or higher than 5*10¹⁹ cm⁻³.

As shown in FIG. 15, an optoelectronic device if is disclosed in accordance with the ninth embodiment. The method for manufacturing the optoelectronic device if incorporates the steps as disclosed in FIGS. 1A˜1C, 13A˜13E and the descriptions thereof. The major difference between the optoelectronic device if shown in FIG. 15 and the optoelectronic device 1 d shown in FIG. 13E is the structure of the first ohmic contact layer 130.

In the ninth embodiment, the first ohmic contact layer 130 comprises a first doping layer 130 a and a second doping layer 130 b between the first doping layer 130 a and the second window layer 112. The first doping layer 130 a and the second doping layer 130 b together may be a tunnel junction structure. The second doping layer 130 b and the second window layer 112 have the same conductivity-type, and the first doping layer 130 a and the second window layer 112 have different conductivity-types. For example, the second doping layer 130 b and the second window layer 112 are p-type, and the first doping layer 130 a is n-type, or the second doping layer 130 b and the second window layer 112 are n-type, and the first doping layer 130 a is p-type. The lowest impurity concentrations of the first doping layer 130 a and the second doping layer 130 b are equal to or higher than 5*10¹⁹ cm⁻³.

In addition, as shown in FIG. 15, the optoelectronic device if further comprises a transparent conductive layer 200 covering the first ohmic contact layer 130 and the second window layer 112. The transparent conductive layer 200 comprises metal oxide, such as indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide. The first pad 171 is formed on transparent conductive layer 200 for conducting electrical current into the optoelectronic device 1 f. The transparent conductive layer 200 may be able to laterally spread the electrical current, and then, the electrical current flows into the second window layer 112 through the first ohmic contact layer 130. From a top-view, the layout of the first ohmic contact layer 130 may comprise a pattern similar to the pattern of the fingers 132 shown in FIG. 6, 8 or 12A, or comprise a plurality of dots which are separates for each other for decreasing the light attracted by the first ohmic contact layer 130 in accordance with the ninth embodiment.

In one embodiment, an optoelectronic device based on the ninth embodiment may comprise a second ohmic contact layer 140′ comprising a tunnel junction structure similar to that of the eighth embodiment.

It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the devices in accordance with the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers combinations, modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.

Although the drawings and the illustrations above are corresponding to the specific embodiments individually, the element, the practicing method, the designing principle, and the technical theory can be referred, exchanged, incorporated, collocated, coordinated except they are conflicted, incompatible, or hard to be put into practice together.

Although the present application has been explained above, it is not the limitation of the range, the sequence in practice, the material in practice, or the method in practice. Any combination, modification or decoration for present application is not detached from the spirit and the range of such. 

What is claimed is:
 1. An optoelectronic device comprising: a semiconductor stack comprising a first surface and a second surface opposite to the first surface; a first contact layer on the first surface; and a second contact layer on the second surface and comprising an impurity concentration increasing in a direction from the semiconductor stack toward the second contact layer, wherein the second contact layer comprises a plurality of dots separating from each other and formed of semiconductor material.
 2. The optoelectronic device of claim 1, wherein the highest impurity concentration is equal to or larger than 1*10¹⁹ cm⁻³, and the lowest impurity concentration is equal to or lower than 1*10¹⁸ cm⁻³.
 3. The optoelectronic device of claim 1, wherein the second contact layer comprises GaP.
 4. The optoelectronic device of claim 1, wherein one of the dots has a width between 5 μm and 15 μm both inclusive.
 5. The optoelectronic device of claim 1, wherein one of the dots has a thickness is between 100 Å˜10000 Å both inclusive.
 6. The optoelectronic device of claim 1, wherein one of the dots comprises a side surface and a top surface substantially parallel to the second surface, wherein an angle between the side surface and the second surface is equal to or larger than 90 degree.
 7. The optoelectronic device of claim 6, further comprising an insulating layer on the second surface and contacting the side surface.
 8. The optoelectronic device of claim 7, wherein the insulating layer covers a portion of the top surface.
 9. The optoelectronic device of claim 7, wherein the insulating layer comprises a refractive index between 1.3˜1.6 both inclusive.
 10. The optoelectronic device of claim 7, wherein the thickness of the insulating layer is equal to or smaller than the thickness of the one of the dots.
 11. The optoelectronic device of claim 6, further comprising a transparent conductive layer on the plurality of dots.
 12. The optoelectronic device of claim 11, wherein the transparent conductive layer has a surface opposite to the plurality of dots, and a roughness average (Ra) of the surface is equal to or lower than 2 nm.
 13. The optoelectronic device of claim 12, further comprising a reflecting layer on the surface of the transparent conductive layer.
 14. The optoelectronic device of claim 13, further comprising a substrate on the reflecting layer.
 15. The optoelectronic device of claim 14, further comprising a metal layer between and bonding the reflecting layer and the substrate.
 16. The optoelectronic device of claim 14, wherein the substrate comprises Si.
 17. The optoelectronic device of claim 15, wherein the metal layer comprises In, Au, Sn, Pb, InAu, SnAu, or the alloy thereof.
 18. The optoelectronic device of claim 1, wherein the second contact layer comprises a tunnel junction structure. 